Soil conditioner trial lifts vining pea yields by nearly 40%

Applying a phosphate enhancer to vining pea seed-beds led to an average yield increase of nearly 40% in Agrii trials carried out in conjunction with a Yorkshire vining pea co-op.

Improved crop establishment and plant health is especially important for the co-op, Swaythorpe Growers, as members look to promote crop resilience to reliably meet weekly processing demand.

See also: How starter fertiliser can raise pulse yields by 17%

Agrii research and development manager Jim Carswell says phosphate lock-up is a widely recognised problem on both high- and low-pH soils.

This is mainly because cations such as calcium, magnesium and iron lock up phosphorus, resulting in only 5-15% of applied P being used by the crop.

In spring cereals valuable improvements have been achieved through better early nutrition, especially with available phosphate. So could the same be achieved in pulses?

Jim says the answer is yes: three years of work with a specially developed P, K and S starter fertiliser with protected phosphate (APP) gave positive crop yield responses in 29 of 35 split-field and Adas tramline trials.

This equated to an average yield increase of 17.27% for peas and beans across five very different sites in the UK and over three seasons.

However, farmers don’t always want to buy fertiliser, so in 2022, Agrii set out to develop a soil conditioner which could be applied to the seed-bed with the pre-emergence herbicide mix.

Jim explains that the liquid phosphate enhancer (Agrii Start Release) is based on tricarboxylic and diphosphonic acids.

It works on the cations in soil that lock up the phosphate, thereby releasing phosphorus into the soil for uptake by roots. He says the product is ideal where soil reserves allow “mining” of the soil phosphate (Index 2+) rather than applying “fresh” phosphate.

Sprayer applying pre-emergence herbicide


This tends to be soils with a higher cation exchange capacity (clays, silts and loams), as they are able to hold larger quantities of phosphate than sands.

The trials, carried out in conjunction with Swaythorpe Growers, showed positive yield responses in all five split-field comparisons over two seasons.

This equated to an average 38.36% yield increase across two very different seasons.

The increased yield was due to a combination of greater pod numbers (4.5%) and the number of peas in each pod (18.9%). Jim also saw better rooting and taller, stiffer canopies.

Crop biomass was higher during the season, and tissue testing showed improved levels of most nutrients.

Vining pea sampling at Ruston Parva on 3 July 2023


Farm standard











Jim adds that the phosphate enhancer tends to be more effective when there is soil moisture. Responses were smaller in 2023, as soils were very dry.

Swaythorpe Growers

The 71-member Yorkshire co-op is unique in being a partner in a carbon-neutral freezing and packing plant, which is set to process 17,500t of peas this year along with other vegetables.

The pea freezing plant near Driffield is next door to an anaerobic digestion plant which supplies all the electricity, while waste water and organic matter are fed back into the digester.

Swaythorpe Growers sells under its own Yorkshire Peas brand, as well as supplying leading retailers and food service customers across the UK and Europe.

Production director Matthew Hayward says the key objective is to keep the plant running at full capacity, and this relies on knowing exactly when to plant and harvest their peas.

Factors such as variety, height above sea level, establishment system and soil type are all taken into account when planning drilling dates to deliver the required tonnage each day.

However, the loss of fungicide seed treatments has meant a greater focus on those soils that tend to be colder in spring.

“We need to get peas up and away as quickly as possible and be healthy plants,” he says.

This is where the phosphate enhancer comes in. Members can use the product this coming season, with the costs borne by the group.

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